If carried out, Sandoval&39;s would be the first lethal injection execution in the midwestern state, which last put a prisoner to death in 1997 using the electric chair.

Like other states, Nebraska has struggled to find the medications it needs for lethal injections. Pharmaceutical companies have bowed to public pressure to stop providing the necessary drugs.

State officials did not disclose where they obtained their drugs for the new protocol, which avoids the use of the hard-to-get sodium thiopental as the primary anesthetic.

Danielle Conrad of the Nebraska chapter of the American Civil Liberties Union called the new protocol "an untested and experimental lethal injection cocktail."

"We are horrified," she said in a statement.

The new protocol consists of the sedative diazepam (commonly known by its brand name Valium), the powerful painkilling narcotic fentanyl citrate, the muscle-relaxant cisatracurium besylate, and potassium chloride, which stops the heart.

The death penalty has had a rocky history in the state. It was outlawed by legislators in 2015, but reinstated by voters through a 2016 ballot initiative.

Executions in the United States have declined over the last 10 years, with 23 carried out so far this year, according to the Death Penalty Information Center.